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IC ^°^2 



Bureau of Mines Information Circular/1986 



Ground Subsidence and Structural Damage 
Over an Abandoned Room-and-Pillar Coal 
Mine at Hegeler, IL 



By Gennaro G. Marino, James W. Mahar, Larry R. Powell, 
and Richard E. Thill 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 9072 



Ground Subsidence and Structural Damage 
Over an Abandoned Room-and-Pillar Coal 
Mine at Hegeler, IL 



By Gennaro G. Marino, James W. Mahar, Larry R. Powell, 
and Richard E. Thill 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Model, Secretary 

BUREAU OF MINES 
Robert C. Morton, Director 







Library of Congress Cataloging in Publication Data: 



Ground subsidence and structural damage over an abandoned room- 
and-pillar coal mine at Hegeler, IL . 

(Information circular / Bureau of Mines ; 9072) 

Bibliography: p. 22-23. 

Supt. of Docs, no.: I 28.27: 9072. 

1, Subsidences (Earth movements)— Illinois— Hegeler. 2. Coal 
mines and mining— Illinois— Hegeler. 3. Mine subsidences— Illinois — 
Hegeler. 4. Earth movements and building— Illinois— Hegeler. I. 
Marino, Gennaro G. II. Series: Information circular (United States. 
Bureau of Mines) ; 9072. 

-^?^&5.U4 [QE600.3.U6] 622s [363.3M97] 85-600363 



^ 




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CONTENTS 



Page 



Abstract 1 

Introduction 2 

Acknowledgments 3 

Site description 3 

Geologic conditions 4 

Regional geology 4 

Site geology 5 

Mining history and practice 6 

Surface subs Idence 7 

Subsidence history 7 

Sag characteristics 7 

Sag Interrelationships 13 

Structural damage 14 

Behavior of house C 14 

Behavior of radio station building 17 

Behavior of radio towers 18 

Building response to sag subsidence 19 

Summary 21 

References 22 

Appendix. — Chronological list of events related to subsidence at Hegeler, IL. . . 24 

ILLUSTRATIONS 

1 . Area location map. 4 

2. Site location map 4 

3. North-south geologic cross section through study site 6 

4. Mine map showing location of subsidence sags 7 

5. Location of subsidence profiles, cross sections, and reference points 8 

6. Sketch map of sag 1 tension and compression features In 1967 9 

7. Existing and assumed presubs Idence, north-south profile 9 

8. Adjusted profiles, slopes, and curvatures for sag 1 10 

9. Adjusted profiles, slopes, and curvatures for sag 2 11 

10. Adjusted profiles, slopes, and curvatures for sag 3 12 

11. Photographs of tension cracks and compression ridges 12 

12. Relationship between mine depth and the subsidence factor 13 

13. Relationship between the subsidence factor and (.4) profile slope and (B) 

average maximum curvature 13 

14. Relationship between maximum tensile curvature and compressive curvature. . 14 

15. Plan of damage to house C 15 

16. Vertical-displacement contours for sag 1 15 

17. North bearing wall of crawl space In house C In 1978 16 

18. Plan of damage to radio station building 17 

19. Postulated progression of subsidence associated with sag 3 18 

20. Relationships between subsidence profile characteristics and ground 

deformations 19 

21. Comparison of subsidence profiles of radio station building and house C... 19 

TABLES 

1 . Summary of sag characteristics 8 

2. Summary of building damage and associated ground movements 20 

3 . Classification of visible damage to walls 21 





UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


ft 


foot mm millimeter 


mi 


mile pet percent 



GROUND SUBSIDENCE AND STRUCTURAL DAMAGE OVER AN ABANDONED 
ROOM-AND-PILLAR COAL MINE AT HEGELER, IL 

By Gennaro G. Marino/ James W. Mahor/ Larry R, Powell, and Richard E. Thill 



ABSTRACT 

The Bureau of Mines and the University of Illinois investigated sur- 
face characteristics and damage to structures from mine subsidence over 
a room-and-pillar coal mine in Hegeler. IL. Data on three adjacent sub- 
sidence sags and associated structural damage were collected, sum- 
marized and evaluated. The subsidence sags developed over a 10-year 
period and took place above a modified room-and-pillar operation mining 
the Herrin (No. 6) coal at a depth of 130 to 135 ft. Surface vertical 
displacements of 3.0 to 3.5 ft resulted from extracting 6.1 to 6.4 ft of 
coal. 

Ground movements associated with sag formation severely damaged three 
houses and a radio station building, broke numerous utility lines, and 
structurally distorted three radio transmission towers. The radio sta- 
tion was remodeled and the towers repaired, but the three houses were 
subsequently demolished. Surface waters collecting in the subsidence 
depressions caused failure of radial ground transmission systems. The 
following subsidence profile characteristics were determined at the ra- 
dio station and one of the houses, respectively: profile slopes, 0.02 
and 0.07; maximum curvatures, 2.3 x 10"'* ft"' and 3.0 x 10~* ft"'; and 
angular distortions, 6.6 x 10"^ and 62.0 x 10"^. Although the house was 
more severely damaged than the radio station, both structures are clas- 
sified as severely to very severely damaged. 

'Visiting research engineer, Dept. of Civil Engineering, University of Illinois at 

Urbana-Champaign, Urbana, IL, 
o 
Geologist, Twin Cities Research Center, Bureau of Mines, Minneapolis, MN. 

•^Supervisory geophysicist. Twin Cities Research Center. 



INTRODUCTION 



Mine subsidence and damage to surface 
structures have been problems in Illinois 
since the start of extensive underground 



mining in the late 1800' s. 



The 



most 

serious problems are associated with 
early room-and-pillar practices. Early 
coal production was obtained from out- 
crops and shallow seams at depths less 
than 100 ft (I) A The extraction scheme 
was characterized by irregular layouts 
and poorly defined areas (2^). In older 
mines, although overall recovery averaged 
about 50 pet, some panel areas are be- 
lieved to have recovered as much as 80 
pet of the coal (3), By 1975, over 4,000 
abandoned underground coal mines were re- 
ported in 70 Illinois counties (4^). A 
considerable number of unidentified small 
mines still exist for which no documenta- 
tion is known. As of 1975, over 800,000 
acres of abandoned underground coal mine 
workings existed in the State (_5). 

Subsidence creates topographic changes 
characterized by tilt, curvature, and 
displacements of the ground surface (6^) . 
Differential movements of the ground sur- 
face cause damage to structures and util- 
ities. By 1976, subsidence was reported 
in 28 municipalities in 18 counties (7^). 
During the first 2 years of operation of 
the Illinois Mine Subsidence Insurance 
Program, mine subsidence was found to be 
the cause and origin of damage to the 
structures in 20 pet of the files closed. 
Cost data for repairs are incomplete be- 
cause about 60 pet of the structures 
still show active movement. Field data 
reveal that damage estimates average 
$20,000 to $30,000 per structure, or to- 
tal property damage of $1 to $2 million 
per year (8^). 

Recently, Illinois mining practices and 
subsidence characteristics were described 
(2^, 9-11) , structural responses to sub- 
sidence profile strains were analyzed 
(12-13) , and the Illinois Mine Subsidence 
Insurance Program was summarized (JB) . 

^Underlined numbers in parentheses re- 
fer to items in the list of references 
preceding the appendix. 



Two reports on subsidence (14-15) have 
been prepared as public information for 
homeowners considering subsidence insur- 
ance. In addition, several reports con- 
taining data on structural reponses to 
subsidence at various sites have been 
published by the Illinois Abandoned Mined 
Land Reclamation Council. 

The nature and extent of damage to sur- 
face structures as a result of subsidence 
movements are not well known in Illinois 
because there has been very little sci- 
entific or engineering documentation of 
subsidence. To date, few structures have 
been monitored and little is known about 
the extent of subsidence effects on the 
land surface, especially farmland (15). 
Because no systematic subsidence profile 
data and accompanying structural damage 
measurements have been coiiq)letely synthe- 
sized, it is difficult to predict the 
critical strains, slope, and curvature 
prevailing at the time of structural dam- 
age. Predictions of differential settle- 
ments and damage potential of buildings 
rely on structure-ground surface inter- 
actions (16-17) . Measurements of differ- 
ential settlement and horizontal strain 
on the foundation and adjacent ground are 
necessary (18-19) . 

As part of a cooperative mine subsid- 
ence research program with the State of 
Illinois, the Bureau of Mines is measur- 
ing the type and severity of subsidence 
damage and ground profile characteris- 
tics to determine the effects of subsid- 
ence on surface lands and structures. 
These data will be used to develop sub- 
sidence prevention, control, and repair 
strategies. First, the mechanics of how 
a structure is affected by subsidence 
must be thoroughly understood. Severity 
of damage with respect to differential 
settlement and tilt must be assessed to 
establish a severity index, which must 
then be verified with respect to the mag- 
nitude of ground movements. In addition, 
valuable information is being collect- 
ed on what causes room-and-pillar mines 
to become unstable and collapse causing 
subsidence. 



The development of subsidence predic- 
tion methodologies will enable Illinois 
coal mine operators to comply with regu- 
lations for protection of surface land 
while maximizing resource recovery. By 
combining the capabilities to precalcu- 
late the subsidence profile and the level 
of damage that may occur to surface lands 
and structures, coal mine operators will 
be able to determine the impacts of un- 
dermining an area and thus be able to 
plan an efficient, economic, and safe 
mine while protecting the surface. 

Terminology for subsidence depres- 
sions is adopted from Bauer and Hunt 
(10). In Illinois, pit subsidence is 
used to describe a depression with near- 
ly vertical to belled-outward walls. 
Pit subsidence is caused by collapse of 
shallow, abandoned mines with incompe- 
tent overburden. Sag subsidence is ex- 
pressed by a large depression with gentle 
slopes. The term "sag" is used to de- 
scribe the nearly equidimensional sub- 
sidence depressions over room-and-pillar 
mines. The term "trough" is reserved to 
describe elongate depressions produced 
over modern longwall and high-extrAction 



room-and-pillar operations. The three 
depressions that developed on the Hegeler 
site are subsidence sags, and this term 
will be used throughout this report. 

The purpose of this study is to docu- 
ment and characterize mine subsidence and 
related damage that occurred over an 
abandoned room-and-pillar mine between 
1967 and 1981. The approach was to col- 
lect, summarize, and evaluate the surface 
ground movements and damge associated 
with three adjacent subsidence events 
in Hegeler, IL. The work included col- 
lecting news articles, personal accounts, 
and documents related to the subsidence 
events; determining the sag configura- 
tions; establishing reference points and 
measuring the existing differential dis- 
placements of the ground and structures; 
and summarizing and evaluating the data. 
Monitoring of the site is continuing. 
Future reports will detail the mining and 
geological conditions relevant to eval- 
uating the mechanisms of mine collapse 
and changes in overburden properties sub- 
sequent to the formation of the subsid- 
ence sags. 



ACKNOWLEDGMENTS 



The results of this report are based on 
work conducted under Bureau of Mines con- 
tract J0205071, initiated under the Min- 
erals Environmental Technology Program. 
The work was performed by the Civil En- 
gineering Department, University of Illi- 
nois at Urbana-Champaign between May 1978 
and June 1981. 

The authors would like to thank 
James Jessop, geophysicist , Twin Cities 
Research Center for support and par- 
ticipation in field activities. The 



cooperation of Mike Mitzloff , Ralph Cox, 
and Allan Thomas of the radio station 
management is acknowledged and great- 
ly appreciated. Robert Bauer and Tony 
DeVine, geologists with the Illinois 
State Geological Survey, supplied infor- 
mation about the site. We would also 
like to thank Paul DuMontelle of the Il- 
linois State Geological Survey for crit- 
ically reviewing the manuscript and pro- 
viding protographs and documentation of 
the early subsidence history at the site. 



SITE DESCRIPTION 



The study site is located in Hegeler, 
IL, which is a few miles south of 
Danville and about 5 mi west of the 
Illinois-Indiana border (fig. 1). Heg- 
eler can be characterized as a light 



industrial and agricultural area with a 
population of about 1,600. The area is 
extensively underlain by roomr-and-pillar 
coal workings that operated between 1870 
and 1974. 




Note: Shoded area is Vermilion County 



FIGURE 1.- Area location map. 

The site is situated in SW 1/4 sec. 29, 
T.19N, R.UW of the second principal 
meridian. Subsidence has affected the 
north side of Spelter Avenue, including 
a radio station and its three transmit- 
ting towers (fig. 2). Farmlands lie to 
the north and east of the property. 
The west side of the property is bound- 
ed by an embankment probably used in 
the past for coal hauling. Other proper- 
ties along Spelter Avenue are residen- 
tial. The topography is flat to gently 
rolling. 




Property 
line 



Spelter Ave. 



LEGEND 
■^ Borehole 
-•- Guy wire and onctior 

100 200 

I I I 



Scale, ft 



FIGURE 2. - Site location map. 



GEOLOGIC CONDITIONS 



REGIONAL GEOLOGY 

Physiographically , Hegeler lies within 
the Bloomington Ridged Plain, a region of 
gently rolling terrain crossed by many 
glacial recessional moraines that form 
low hummocky ridges that trend in a gen- 
eral east-west direction. In east cen- 
tral Illinois, the bedrock has been cov- 
ered serveral times by large continental 
glaciers during the Pleistocene Series. 
The surficial deposits include glacial 
drift deposited during the Wisconsinan, 
Illinoian, and Pre-Illinoian glacial 
stages (20) . The drift is a complex se- 
ries of units, including till, which is 
primarily a heterogeneous mixture of 
sand, gravel, and pebbles in a compact 



clay and silt matrix. The thickness of 
the tills is generally 10 to 20 ft in the 
study area. 

Structurally, the area is situated on 
the northeastern margin of the Illinois 
Basin. The basin contains marine and 
nonmarine Pennsylvanian age sediments 
that thicken toward southeastern Illi- 
nois. The site is located in a broad 
gentle depression known as the Marshall 
Syncline, which is bounded on the east 
by the Cincinnati Arch and on the west 
by the LaSalle Anticlinal Belt (21). 
Most of the anticlines and synclines are 
wide, gentle, and open, and the strata 
dip 1° or 2°. However, occasional dips 
of up to 15° are found on more prominent 
structures (22). 



The strata in east central Illinois are 
essentially flat-lying interbeds of sand- 
stone, shale, coal, underclay, and lime- 
stone that were deposited as part of 
large deltas in a gently subsiding basin 
(23) » The marine, brackish water and 
delta plain sediments have complex rela- 
tions making interpretations of their 
depositional environments difficult. In 
the Hegeler area, sandstone and limestone 
are much less abundant than in adjacent 
areas (24). Frequent and abrupt changes 
in rock type over relatively short dis- 
tances are characteristic of coal measure 
rocks in Illinois. 

The rocks immediately underlying the 
study area are part of the Modesto and 
Carbondale Formations (fig. 3). The Dan- 
ville (No. 7) coal is at the top of 
the Carbondale Formation. It varies in 
thickness from 2.5 to 5.5 ft and has 
been mined locally (25) . The Farmington 
Shale is the lowest named unit of the 
Modesto Formation, located above the 
Danville (No. 7) coal. It is commonly a 
gray shale that becomes coarser grained 
upward. The Carbondale Formation con- 
tains the Herrln (No. 6) coal, which is 
located 120 to 150 ft below the surface 
in the Hegeler area. It is generally 6 
ft thick and overlain by grayish-black 
shale. Rock units below the Herrin (No. 
6) coal consist of an underclay over the 
nodular Higgensville Limestone followed 
by a shale and then the Vermilionvllle 
Sandstone. 

SITE GEOLOGY 

The geology beneath the site was de- 
termined by drilling five exploratory 
boreholes to depths ranging from 147 to 
159 ft. The locations of these bore- 
holes are shown in figure 2. Split-spoon 
samples were taken in the glacial till 
at 5-ft intervals, continuous NX core 
was obtained in the rock, and thin-walled 
tube samples were recovered from the 
underclay. A north-south geologic cross 
section across the site, developed from 
the five boreholes, is given in figure 3. 

Glacial till, 30 to 47 ft thick, lies 
directly on the bedrock surface, which 
forms a gentle bedrock valley centered 



near the north end of the site. The 
grain size distribution of the till 
varies across the site, but no particles 
greater than medium-size gravel were re- 
covered in the split-spoon samples. Gen- 
erally, the till consists of two major 
units. The first unit is a thick layer 
of dense, coarse-to-fine sand with some 
clayey silt and medium gravel surrounded 
by the second unit, which consists of 
silt and clay. A small lens of dense, 
coarse-to-fine sand with some fine gravel 
and silt exists near the bedrock surface 
at the north end of the site. 

The Farmington Shale is present below 
the glacial tills and is the first bed- 
rock unit encountered in the boreholes. 
The upper part of the shale, consisting 
of interbedded shale and siltstone, was 
encountered only at the south end of the 
site. Generally, the Farmington Shale is 
a gray silty shale with both clayey seams 
and thin siltstone bands that become more 
frequent toward the base of the unit. In 
boreholes B-2 and B-5, the lower part of 
the Farmington Shale above the Danville 
(No. 7) coal is a thin lens of black car- 
bonaceous shale. 

The Danville (No. 7) coal ranges from 4 
to 7 ft thick and lies 80 to 88 ft below 
the surface. It thins and contains more 
impurities below the black carbonaceous 
shale. A 6- to 7.5-ft-thick underclay, 
which grades into a nodular limestone, 
lies below the coal. 

The next unit, the Energy Shale, con- 
sists of a sequence of three grayish 
siltstones, which change from a laminated 
siltstone at the top to a thinly bedded 
siltstone with clay layers at the bottom. 
The unit is 29 to 35 ft thick, and indi- 
vidual facies range from 4 to 23 ft 
thick. 

The Herrin (No. 6) coal is 6 to 7 ft 
thick at depths of 131 to 135 ft below 
the surface. The seam has a westerly dip 
of about 1.2 pet. The underclay is a 
green-to-gray clayey shale that contains 
limestone nodules and grades into a dis- 
continous argillaceous limestone. Below 
the limestone is a 9- to 13-ft-thick gray 
shale. The lowest rock unit drilled into 
at the site is the Vermilionvllle Sand- 
stone. It is a gray-to-green siltstone. 



No 
650 

625 

*". 600 



< 

> 

LJ 

_J 
Id 



UJ 
> 

UJ 



< 
111 
en 



rth 



B-3 



575 



550 



525 



500 - 



475"- 




Silty shale 

Coal 



Silt and clay with some sand and^gravei 



;iaY wiin some sana ana gravel ^^-^ ^ i, — j 

Silty shale 
^^Carbonaceous shale 




Nodular limesfo^ 



Calcareous clayey shale- 5j,ly ghole 

Siltstone 



100 200 

_J I 



Glacial drift 



Formington Shale 



nanville INo. ^)ronl 



Underclay 



Energy Shole 



Herrin (No.6) coal 



Underclay 
^ioainsvineXimestone 



Cioysfone Shale 



Vermilionville Sandstone 



r 



Scale, f1 



FIGURE 3. - North-south geologic cross section through study site. 



The groundwater table generally lies 
within 10 ft of the ground surface. 
Based on the borehole data, there are no 



good soil or bedrock aquifers 
ft of the ground surface. 



within 150 



MINING HISTORY AND PRACTICE 



The mine that underlies most of the 
town of Hegeler, and an extensive area 
north of the site, worked the Herrin (No. 
6) coal from 1946 to 1974. The site was 
undermined from 1960 to 1967. The mine, 
the last operating deep shaft in the 
area, was closed in 1974. 

The 6- to 7-ft-thick coal seam was 
mined using a modified room-and-pillar 
operation (2^) with mine openings oriented 
north-south and east-west (fig. 4). At 
the project site, working entries were 
driven westward from the south main. 
Panels were then developed southward from 
east-west working mains. A 250-ft wide 
barrier pillar borders the north edge 
of the site. After 1953, pillar robbing 
was not practiced, but as much coal as 



possible was taken at the working face, 
contingent upon the stability of the 
mine opening. The roof of the mine was 
supported with timber props, and the 
ratio of timber to mined tonnage was 
high, which indicates stability problems 
in the immediate roof. 

In the study area, the mine has rec- 
tangular pillars ranging in width from 
10 to 25 ft, rooms 20 to 45 ft wide, and 
crosscuts 10 to 25 ft wide (fig. 4). The 
crosscuts were made about every 85 to 
160 ft. The pillar height-to-width ratio 
ranges from 0.24 to 0.64 and panel width 
to depth ratios range from 1.9 to 2.8. 
Under the site, the extraction averages 
70 pet with some variation due to differ- 
ent extractions in entries and panels. 



SURFACE SUBSIDENCE 



SUBSIDENCE HISTORY 

Three subsidence sags have developed in 
the study area between 1967 and 1978. 
The locations of the sags occurred above 
areas of high extraction (fig. 4). Sub- 
sidence has progressed northward starting 
with sag 1 in 1967, sag 2 in 1968, and 
sag 3 between 1976 and 1978. The sags 
range from 240 to 570 ft in diameter. 
Sag 1 encompasses the radio station 
building and an area to the south and 
west. Sags 2 and 3 developed north of 
the building in the field containing the 
transmission towers. Sags 1 and 2 sub- 
sided with one main event, but sag 3 de- 
veloped in two or more major events in 
which the ground movements have pro- 
gressed westward. A summary of the sub- 
sidence history at the study site can be 
found in the appendix. 

Sag 1 started to develop in the vicin- 
ity of the radio station about noon on 
July 21, 1967. The subsidence eventually 
encompassed the access road and parking 
lot and the surrounding area. The ground 
movements damaged three houses, the radio 
station, and service utilities to these 
structures (26-29) . In addition, the 
southern guy wires to tower 1 were ten- 
sioned. The maximum settlement (about 
3.5 ft) occurred over an area west of 
the radio station parking lot and access 
road. Although most of the displacement 
occurred within 2 days, ground movements 
were reported as late as October 1967. 
Then, in May or June 1969, the northern 
portion of the radio station building 
sustained additional damage from resid- 
ual movements in the northern portion of 
sag 1. 

Sag 2 develop in the field north of the 
radio station building in May or June 
1968. The center of the sag is located 
40 ft northwest of tower 1. Most of the 
settlement (3 ft) occurred rapidly within 
6 weeks. Tower 1 subsided 2.75 ft, which 
caused the guy wires supporting the tower 
to loosen, and they had to be retightened 
several times. Surface water collected 
in the sag around tower 1. 

In November or December 1976, sag 3 de- 
veloped under tower 2. The tower nearly 
failed when it settled and tilted 0.05 ft 




O 100 200 

I , 1 

Scale, ft 



Barrier 
pillar 

LEGEND 

o Tower 

^ Coal pil lar 

IT-IT Sag limit 



FIGURE 4. - Mine map showing location of sub- 
sidence sags. 



to the east. In July 1978, residual sub- 
sidence of sag 3 produced settlement and 
lateral movement of the southwest guy 
wire anchors for tower 3. The upper 150 
ft of the tower was bent in response to 
the ground movements. The maximum set- 
tlement was about 3 ft. 

SAG CHARACTERISTICS 

Level surveys were run across each sag 
to determine apparent maximum vertical 
ground displacements. Each sag was sur- 
veyed at least twice. Horizontal ground 
movements were also measured periodically 
using a tape extensometer stretched be- 
tween posts supporting the transmission 
line and reference points on the radio 
station building (fig. 5). Because sur- 
vey results indicated that no significant 
horizontal displacement has occurred be- 
tween late 1978 and 1981, no further dis- 
cussion will be necessary. 




LEGEND 
Tower 

Guy wire and anchor 
Trough limits 



FIGURE 5. - Location of subsidence profiles, 
cross sections, and reference points. 

The limits of subsidence were deter- 
mined from (1) a map of perimeter tension 
cracks and compression ridges prepared 
by the Illinois State Geological Survey 
(31) in 1967 (fig. 6), (2) accounts of 
damage from interviews with radio sta- 
tion personnel and owners of the damaged 



structures in the area, (3) measured dif- 
ferential settlement of the radio station 
building, and (4) field work by project 
personnel. Ground surface profiles prior 
to subsidence were estimated by inter- 
polating linearly across the access road 
and parking lot to points outside the sag 
(fig. 7). The profile for sag 1 is lo- 
cated 100 ft east of the center of the 
sag and was measured after resurfacing of 
the parking lot. 

For sags 2 and 3, profiles were pre- 
pared from elevations measured on a 20- 
to 25-ft grid in order to establish the 
postsubsidence profiles. The presubsid- 
ence profiles were determined by linearly 
interpolating between the apparent limits 
of sags and known presubsidence eleva- 
tions of reference points inside the 
sags. The following were taken into con- 
sideration in drawing the profiles: the 
drainage ditch as a low point, measure- 
ments on the settlement of the tower 
bases, and estimated limits of the sags 
as discerned from the postsubsidence 
elevations. 

The adjusted displacement profiles of 
the sags are presented in figures 8 
through 10, and their locations are shown 
on figure 5. The adjusted vertical dis- 
placement is the estimated elevation 
prior to subsidence minus the respective 
subsidence profile elevations. The ad- 
justed vertical-displacement profile was 
determined by drawing a smooth curve 
through points of known settlement. 
Slopes and curvatures were calculated 
based on the adjusted vertical displace- 
ment profile and are plotted below 
the corresponding settlement profiles. 
Table 1 summarizes sag characteristics. 



TABLE 1. - Summary of sag characteristics 



Sag No, 



Maximum diameter f t. . 

Minimum diameter f t. . 

Maximum settlement f t. . 

Maximum slope 

Maximum curvature, ft"^: 

Compression (+) 

Tension (-) 

Extraction pet. . 

Seam height f t. . 

Settlement to extraction height ratio 

Mining depth f t. . 



1 



1.2 
1.2 



350 
310 
3.5 

0.055 

: 10-3 

: 10-5 

66 

6.4 

0.55 

130 



8.6 
7.0 



450 

240 

3.0 

0.038 

; 10-4 

: 10-4 

74 

6.4 

0.47 

130 



6.3 
6.4 



570 

410 

3.0 

0.034 

: 10-4 

: 10-4 

71 

6.1 

0.50 

135 



LEGEND 

— — Tension fractures 
— - Compression ridges 
Sag limit 




FIGURE 6. - Sketch map of sag 1 tension and compression features in 1967. 

(Courtesy of Illinois State Geological Survey.) 



■Spelter Ave 




< 

UJ 



KEY 
Presubsidence profile 



South 



642 



Tower 3 



North 



200 



400 600 800 

HORIZONTAL DISTANCE, ft 



1,000 



1,200 



FIGURE 7. - Existing and assumed presubsidence, north-south profile. 



10 



Vertical displacement 



Vertical displacement 



400 




Vertical displacement 



100 



200 



300 



400 




50 100 160 200 250 300 



50 100 150 200 250 




Curvature 



1 00 200 300 

HORIZONTAL DISTANCE, ft 



Too 



-4 - 
-8 - 
-10 



Compression 



Tension 




Curvature 



50 100 150 200 250 

HORIZONTAL DISTANCE, ft 



6 
4 
2 

-2 
-4 




Compression 



Tension 



50 100 150 200 250 300 
HORIZONTAL DISTANCE, ft 



FIGURE 8. - Adjusted profiles, slopes, and 
40=ft lengths from survey data. Surveyed Nov 



curvatures for sag 1. Profile slopes and curvatures calculated on 
, 11, 1978. 



Sag 1 is a 290- by 350-ft semirectangu- 
lar depression with rounded corners. 
The area of maximum settlement is approx- 
imately concentric to sag limits. A 
maximum settlement of 3.5 ft is located 
100 ft west of profile A-A' (fig. 8). 
The ratio of settlement to extraction 
height, known as the subsidence factor, 
is 0.55. 

The maximum slope^ in sag 1 is 0.055 
and occurs on the southeast side where 

^Slope is a ratio between any like 
units of length or distance (feet to 
feet, inches to inches, etc, ) . 



house C was located (fig. 8, B-B'). 
Slopes decrease to the north. Around 
the radio station building, the maxi- 
mum slope is roughly 0.02. Both 
structures are located in the tension 
zone but on opposite sides of the sag. 
Curvatures , corresponding to the maxi- 
mum tension and compression, are 1.2 x 
10~5 ft~^ on the south side of the sag 
and 2.0 to 4.0 x 10"^ ffl on the north 
side. Figure 11 shows tension cracks 
and compression ridges associated with 
sag 1. 



11 



Tower I-, Vertical 




200 250 



Tower In 




Vertical 
displacement 



X 



E' 



Host 



-L 



50 100 150 200 250 300 350 400 450 500 





150 200 250 300 350 400 450 500 



250 300 



10 

8 

6 

4 

2 



-2 

-4 

-6 

-8 



- 


1 1 1 1 1 

^^ /^Curvature 


- 


- 


/ Compression \ 


- 


i 


/ Tension \ > 


/ 


-J 


1 1 1 1 1 


- 



50 100 150 200 250 
HORIZONTAL DISTANCE, ft 



300 



4 
3 
2 
I 



I 

-2 

-3 

-4 



1 1 


III III 

/^Curvature >^ 


1 1 




f Compression \ 


- 




Tension \ 




- / 




y^^y^'Vj: 


V 


III III 


1 1 



50 100 150 200 250 300 350 
HORIZONTAL DISTANCE, ft 



400 450 500 



FIGURE 9. - Adjusted profiles, slopes, and curvatures for sag 2. Profile slopes and curvatures calculated on 
40-ft lengths from survey data. Surveyed July 9, 1981. 



Sag 2 is a 450- by 240-ft elliptical 
depression elongated in the east-west di- 
rection. The sag enconpasses the base of 
tower 1 and most of its guy wire anchors. 
The adjusted displacement profiles (fig. 
9) show the sag to be a bowl-shaped de- 
pression with a maximum settlement of 
about 3 ft. 

Slopes for sag 2 are greatest along the 
north-south profile (fig. 9, D-D') where 



the maximum slope is 0.038. This value 
is 1.5 times greater than the maximum 
slope in the east-west direction. The 
maximum curvatures are 8.6 x 10"'* ft~^ in 
the compression zone and 7.0 x 10"'* ft"^ 
in the tension zone. Both occur along 
the north-south profile and are about 
twice those in the east and west portions 
of the sag. 



12 




LJ 
(E 

< 
> 

o 



2 - 



1 

n 


1 1 1 1 

Curvature 


- 


-/I 


i/\ 


Compression 


/ 


v/ 


TensiorN^ 


J, 


v 

1 1 1 1 


1 1 1 



50 100 150 200 250 300 350 400 



50 100 150 200 250 300 350 400 450 
HORIZONTAL DISTANCE, ft 




Tension. 



50 100 I 50 200 250 300 350 400 
HORIZONTAL DISTANCE, ft 



H 



Tower Z-\ 



H' 





1.0 
2.0 
3.0 



0.04 

.02 



-.02 



I I I r] r 
Vertical displacement 

LWest 

75 1 50 275 300 375 450 525 600 




1 


1 1 1 1 1 1 

Slope 


A/ 

1 1 1 M 1 1 1 


75 


150 275 300 375 450 525 6C 



I I I I 
Curvature 

Compression _ 




75 1 50 275 300 375 450 525 600 
HORIZONTAL DISTANCE, ft 



FIGURE 10. - Adjusted profiles, slopes, and curvatures for sag 3. Profile slopes and curvatures calculated on 
40-ft lengths from survey data. Surveyed July 9, 1981. 





FIGURE 11, - Photographs of 0.33-ft-wide tension cracks (A) and 0.25-ft-high compression ridges (B) from 
sag 1 on June 24, 1967. (Courtesy of Illinois State Geological Survey.) 



13 



Sag 3 is oval with a maximum east-west 
diameter of 570 ft and a minimum north- 
south diameter of 411 ft. The sag encom- 
passes nearly all of tower 2 and the 
southern guy wire anchors of tower 3. 
Figure 10 shows that in the north-south 
direction, the sag has a uniform smooth 
profile (F-F' and G-G'), but in the east- 
west direction, the sag bottom varies by 
1 ft or more (fig. 10, H-H'). The maxi- 
mum settlement is 3.0 ft. 

The maximum slope for sag 3 is 0.034, 
which occurs on the south side of profile 
G-G' (fig. 10); however, slopes greater 
than 0.02 exist in many other areas of 
the sag. Curvatures in the compression 
and tension zones are 6.0 x 10~* ft~^ and 
occur in the western part of the sag, but 
in the eastern part they are as great as 
4.0 X 10"^ ft"'. Both slopes and curva- 
tures are erratic in the east-west direc- 
tion and reflect the nonuniform settle- 
ment profile across the bottom of the 
sag. 

SAG INTERRELATIONSHIPS 

The three sags developed above the same 
mine and in similar geologic conditions. 
Sags 1 and 3 are above working panels , 
have semirectangular shapes , and are 
bounded on the north by working entries, 
and on the south and west by barrier pil- 
lars (fig. 4). They have displacement 
profiles with relatively flat centers and 
nearly equal curvatures in the tension 
and conq)ression zones. On the other 
hand, sag 2 occurred over a working entry 
bounded by a barrier pillar on the north 
and wide pillars on the south. It has a 
distinct bowl-shaped profile with the 
maximum compressive curvature greater 
than the maximum tensile curvature. Sag 
3 is the largest, but probably consists 
of two overlapping sags or an initial 
small sag that progressively enlarged. 
Sag 2 is the smallest and has its long 
axis parallel to the underlying working 
entry. 



<j fi - 





1 




1 

KEY 








O Data 


from Peng (JO 




.8 




▼ Hegeler data 






O 








.6 


Sag2^0^^ 










Sag 3-^OT 


O 


O 




.4 


o oa 


o ° 


o 


_ 




o 


CP 


o 






Qo 


8 


°o O 




.2 


O 

o 

1 




OqO 

1 


o_ 



200 



400 



600 



DEPTH, ft 



FIGURE 12. - Relationship between mine depth and 
the subsidence factor. 







1 


° 


A 


1 

Sag 1 








Sag 


6 


*Sag 2 


.4 


° 9, ° 








KEY 




o % 


O 






° Data from Hunt (<?) 


.2 


oo o 


1 






* Hegeler data 

1 



0.02 0.04 

PROFILE SLOPE 



0.06 



0.6 



.2 - 



-1 1 r — I I I 1 1| 1 1 1 1 — I I III 



■ Sag I 



Sag 3 * 



• Sag 2 



10 100 1,000 _ 10,000 

AVERAGE MAXIMUM CURVATURE, 10 ft" 

FIGURE 13. - Relationship between the subsidence 
factor and (A) profile slope and (B) average maximum 
curvature. 



14 



In figure 12, the subsidence factor is 
plotted against mine depth for subsid- 
ence cases over Illinois room-and-pillar 
mines. The Hegeler subsidence sags are 
comparable with other subsidence sags at 
similar mining depths in Illinois. The 
general trend of the plot shows decreas- 
ing subsidence with increasing depth. 

In general, the maximum slopes and cur- 
vatures of subsidence sags tend to in- 
crease with increasing subsidence fac- 
tors. These relationships are shown by 
Hunt (2) for subsidence profiles in Illi- 
nois. The sags at the Hegeler site, how- 
ever, are more severe than those studied 
by Hunt (fig. 13). 

Figure 14 shows that maximum tension 
and compression are almost equal in cases 
of Illinois mine subsidence above aban- 
doned room-and-pillar mines. However, 
when compared with data from other Illi- 
nois mines , the Hegeler sags are much 
more severe. 



1 0,000 FT 



O 

i^' 1,000 



100 



-l 1 — I — I — I I 1 1 



-1 1 — I — I — I r 1 1 



0% 

. °8 



-\ r — I — I — TT- 



A Sag I 
A Sog2 



Sog 3 



KEY 
O Data from Hunt [2) 
A Hegeler data 



-J I I I I I 1 1 



_j I I I I I I 



100 



1,000 



MAXIMUM COMPRESSIVE CURVATURE, 10 ft 



10,000 



FIGURE 14." Relationshipbetween maximumtensile 
curvature and compressive curvature. 



STRUCTURAL DAMAGE 



Damage caused by the three sags oc- 
curred before initiation of the study. 
Data on damage associated with sag 1 are 
based on newspaper accounts, personal in- 
terviews, an Illinois State Geological 
Survey report (31) , and observation of 
the structures. Damage information re- 
lated to sags 2 and 3 were obtained from 
radio station personnel and observations. 

Newspaper accounts (26-29) on sag 1 re- 
ported that gas and water lines were 
broken and telephone lines were pulled 
away from the houses. Houses were de- 
scribed as "leaning" toward the center of 
the sag. Foundations were cracked and 
window and door frames were distorted. 
The radio station floor and walls were 
cracked, windows and doors were distort- 
ed, and the rear of the building was sep- 
arated from the foundation. 

Two houses (A and B) affected by sag 1 
were abandoned and removed before 1975. 
A third house (C) was removed in 1978 
after damage observations were recorded. 
The locations of these houses are shown 
in figure 5. The radio station was in- 
spected after it was remodeled. The be- 
havior of house C and the radio station 
due to subsidence is described in the 



following sections. Houses A and B are 
not discussed because of insufficient 
data. Behavior of the radio towers in 
response to subsidence is presented, fol- 
lowed by a comparison of structural dam- 
age to the nature of the subsidence 
profiles. 

BEHAVIOR OF HOUSE C 

Subsidence damage to this structure was 
described and recorded during May 1978. 
It was a two-story structure with a par- 
tial basement and crawl space (fig. 15). 
The superstructure was wood-framed with 
interior walls made of plaster on wood 
lathe and supported on bearing walls two- 
bricks thick. No attachment was found 
between the bearing walls and the super- 
structure. The foundation consisted of 
three-brick thick wall footings. 

The house was located in the tension 
zone just inside the southeast corner 
of sag 1 (fig. 6). Vertical-displacement 
contours related to sag 1 are shown in 
figure 16. The ground movements subject- 
ed the house to large horizontal strains, 
angular distortions, rigid body tilt, and 
translation. Profile B-B' in figure 8 



15 



Plan view (lower level) 



r~0.O83-0.l67 ft 



T'op . — Windows 

oqr 



Section A-A 

Superstructure! 

—jj— 0.146ft 

Brick wall ^ 

Section B-B' 



Top View 




rr^^^o.073 ft 

0.063 ft 



Section C-C' 



Top view 




Guy wire for tower I 



1.5 fH ^nmirniir 

'- ^1 0.25fl/ 



V = O.Oft 
H = O.I67ft 



KEY 

V Vertical displacement 
H Horizontal displacement 




v=0.083 ft 
H=O.III ft 
V/H=0.75 



V 0.042 ft 

H=0.15fl 

V/H<0.2B 



™,r? 



i!b_ 



Section D-D 



Section E-E 



FIGURE 15. - Plan of damage to house C. The dam- 
age was measured in May 1978. (Sections shown are 
not to scale.) 

shows that the maximum slope and curva- 
ture of the sag in an east-west direction 
occurred within the length of the house. 
The differential settlement across the 
structure was 0.75 ft from north to south 
and 1.0 to 1.5 ft from east to west. 

The bearing walls and on-grade members 
cracked, separated, and tilted in re- 
sponse to the ground movements. Cracks 
opened as much as 0.33 ft, and walls sep- 
arated as much as 1.5 ft. The west brick 
wall of the crawl space tilted, settled, 
and moved laterally away from the super- 
structure (fig. 15, sec. D-D'). At the 
north end, it separated horizontally 1.5 
ft and vertically 0.58 ft from the in- 
terior bearing wall. These wall dis- 
placements occurred because there was no 
foundation-superstructure attachment be- 
tween the exterior and interior walls. 
The vertical separation prevented the de- 
velopment of frictional resistance be- 
tween the sill and wall, thus there was 
essentially no restraint against outward 
movement. Most of the damage to the west 



Radio station building 




louse C 



LEGEND 
o Survey points 



FIGURE 16. - Vertical-displacement contours for 
sag 1. Survey performed in November 1978. 

wall was caused by differential rigid 
body tilt. 

The relationship between profile slope 
and wall tilt is illustrated by the wall 
separations and crack widths in the 
northwest corner of the basement (fig. 
15, sec. E-E'). Here crack widths and 
wall separations are two to three times 
greater at the top than at the bottom. 
The average tilt of the north and west 
walls is estimated to be about 0.08. 
This is comparable to the slope of 0.07 
calculated for this section of the sag. 

Figure 17 shows the western part of 
the north interior wall of the crawl 
space (also figure 15, section D-D'). 
The ground movements produced two major 
diagonal cracks in the wall. At floor 
level, the west crack opened 0.11 ft 



16 




FIGURE 17. - North bearing wall of crawl space in house C in 1978 (looking north). The picture shows the 
change in the nature of separation of the two cracks in the west portion of the wall. Refer to section D-D* in 
figure 15. 



horizontally, and the east crack opened 
0.15 ft. Both cracks increased about 
0.08 ft in width from bottom to top in 
response to rigid body tilt. The western 
crack had a vertical displacement of 0.08 
ft that developed as a result of angular 
distortion. The eastern crack was af- 
fected more by horizontal ground move- 
ment. This is demonstrated by comparing 
the ratios of the vertical-to-horizontal 
crack width (V/H) , which is 0.75 for the 
west crack and 0.28 for the east crack. 
The west crack also has 0.17 ft of north- 
south offset at the top. 

Figure 15, section C-C , shows that the 
south bearing wall has undergone dis- 
placements similar to the north wall. 
The crack in the south wall has a low 
vertical-to-horizontal displacement ra- 
tio. Measurements of the vertical crack 
separation on both the north and south 



walls are consistent with vertical- 
grcJund-displacement contours, which de- 
crease in a southerly and westerly 
direction. 

During subsidence, the eastern portion 
of the superstructure was supported on 
bearing walls, but on the west side, 
the bearing walls settled and moved away 
from the structure. The ground movements 
caused the superstructure to be canti- 
levered out from the east bearing walls. 
The rigidity of the interior walls helped 
transfer the loads and allowed the frame 
to cantilever out over the north and west 
bearing walls. A vertical separation of 
0.6 ft was measured between the north end 
of the west wall and the superstructure. 
The loss of support caused severe distor- 
tion at the window and door frames, and 
bending stresses caused tensile cracks 
and separations. 



17 



Because there was no connection be- 
tween the superstructure and the founda- 
tion, the north and west sides of the 
house were dragged down and moved later- 
ally with the foundation walls. The ab- 
sence of connections eventually allowed 
the superstructure to separate from the 
foundation and to undergo little or no 
lateral strain in response to the wall 
extensions because the frictional resist- 
ance along the wood-brick interface was 
negligible. 

The northward horizontal ground move- 
ment caused the superstructure to move 
north with respect to southern foundation 
walls. A horizontal offset of 0.15 ft 
was measured between the superstructure 
and the west end of the south bearing 
wall (fig. 15, sec. B-B'). 

BEHAVIOR OF RADIO STATION BUILDING 

The radio station building is a 
masonry-block wall structure founded on 
wall footings. The floor consists of a 
wire-mesh-reinforced concrete slab on 
grade. The building is located in the 
northeast section of sag 1 where the hor- 
izontal ground movements were primarily 
extensional (figs. 6, 9). 

The subsidence profiles indicate that 
settlement across the building ranged 
from 0.16 to 1.64 ft. A maximum differ- 
ence in elevation of 1.38 ft was found 
from the northeast to the southwest cor- 
ners of the building. The calculated 
slope between these two corners is 0.02, 
which is comparable to sag profile slopes 
of 0.016 and 0.022 (fig. 8, A-A' and 
C-C). The maximum tensile curvature 
through the building is 2.6 x 10"^ ft"^ 
in a north-south direction and 2.8 x 10"* 
ft~1 in an east-west direction. 

The southwestward horizontal ground 
movements caused cracking and separation 
of the foundation and floor slab. A ver- 
tical crack in the concrete floor opened 
0.167 ft and is oriented subparallel to 
the vertical-displacement contours (fig. 
18, sec. A-A'). The superstructure was 



elevotjon 1.36 ft 




Addition built in 
.968 

Relative elevotion 
0.0 ft 




-Concrete floor slob 
-Wall footing 

Section A-A' 



]v:^ 



Section B-8 



Scale, ft 



Separation greater 
at top 



Top view 



-Concrete pad 
Section C-C' 



,, BiocK 1 
^r^^off 

-^■^0.004-0.167 ft wide 



Section D-D 



FIGURE 18. - Plan of damage to radio station 
building. The damage is not inclusive. The rel- 
ative elevations on the structure were surveyed 
on July 30, 1967. 

displaced horizontally along with the 
southern part of the foundation. On the 
north wall, the superstructure failed in 
shear along the mortar joint just above 
the foundation and was offset 0.083 ft 
southward relative to the footing. In 
addition, the southwest corner of the 
building was offset by the southwest 
movement of the foundation. The super- 
structure appears to have been subjected 
to angular distortion and tension. The 
torsional deformation was produced by a 
change in direction and magnitude of 
ground movements from south to southwest 
within the building. 

About 80 to 90 pet of the damage oc- 
curred within 2 days after the initial 
movement. The damage included jammed 
doors and windows, a tilted front wall, 
and cracks in the floor slab, foundation, 
and exterior masonry block walls. Sev- 
eral months later, the building was re- 
modeled. This work included a false 
floor, interior repairs, exterior siding, 
and a brick facade. A permanent shoring 
system was also installed to support the 
south wall. 



18 



BEHAVIOR OF RADIO TOWERS 

The three radio towers are 200-ft high 
steel truss structures with pin con- 
nections to concrete footings. The foot- 
ings are 6-ft-square concrete blocks em- 
bedded 4 ft in the ground. Four sets of 
four guy wires oriented orthogonally to 
one another prevent the towers from sway- 
ing excessively and overturning (fig. 2). 
Ground subsidence structurally damaged 
all three towers and has caused the guy 
wires to be replaced and/or retensioned 
numerous times. 

Tower 1 was affected by ground move- 
ments associated with the formation of 
sag 1 in 1967. The southwestern-most guy 
wire anchor was displaced toward the cen- 
ter of sag 1, which tensioned the guy 
wire and pulled the top of the tower 
southwestward. Tower 1 was next affected 
by formation of sag 2 in 1968: The tower 
base, which was located near the center 
of the sag, settled 2.6 ft. In addition, 
most of the guy wire anchors settled and 
moved toward the tower base. All of the 
guy wires had to be tightened three times 
before the ground movement stopped. Be- 
tween 1978 and 1981, no additional set- 
tlement of the tower has been measured. 

The formation of sag 3 affected towers 
2 and 3. The eastern part of the sag 
developed in late 1976. It encompassed 
the base of tower 2, most of its guy wire 
anchors, and the southeast set of guy 
wire anchors for tower 3 (fig. 19). In 
addition to settlement, the base of tow- 
er 2 tilted 0.5 ft and moved northeast. 
At this time, most of the tower 2 guy 
wires were loose, and failure of the tow- 
er was a major concern. The southeast 
guy wires of tower 3 tightened as their 
anchor blocks were pulled southward by 
the ground movements. Guy wire adjust- 
ments were made twice, and new ground 
transmission wire systems were installed 



Jl \' 




Scale, ft 



LEGEND 
1976 limits 
1978 limits 
Coal pillar 
Tower 
Guy wire and anchor 



FIGURE 19. - Postulated progression of subsidence 
associated with sag 3. 

for towers 1 and 2. In early 1978, the 
guy wires for tower 2 were replaced. 

In July 1978, additional subsidence oc- 
curred, and sag 3 developed in a west- 
erly direction (fig. 19) . The renewed 
subsidence caused additional settlement 
of the tower 2 base. The cumulative set- 
tlement of the tower 2 base is 2.5 ft. 
The additional movements in sag 3 pro- 
duced tightening of tower 2 and 3 guy 
wires. The upper 150 ft of tower 3 was 
bent as a result of the southwest pull of 
the guy wire anchor blocks. Guy wires to 
both towers were retensioned. 

Surface waters collected in sags 2 
and 3 as a result of subsidence-induced 
modifications to the surface drainage 
pattern. The water caused transmitting 
problems in the ground wire systems. 
These areas were drained and landscaped 
in the summer of 1981. 



BUILDING RESPONSE TO SAG SUBSIDENCE 



The behavior of a structure in response 
to subsidence depends on the location 



and orientation of the structure in the 
subsidence sag, the character of the 



19 



ground movements, the structural charac- 
teristics and interaction effects, the 
presence of construction joints, and pre- 
vious deformation history (12) . Subsid- 
ence characteristics are usually defined 
in a two-dimensional profile showing the 
vertical displacement, slope, and curva- 
ture (fig. 20) . Compression occurs where 
the lateral ground displacements decrease 
in the direction of lateral ground move- 
ment, whereas extension exists where 
ground displacements increase in the di- 
rection of lateral movement. 

Sags develop differently over room-and- 
pillar mines In Illinois than over modern 
high-extraction operations. The movement 
of a longwall face or pillar extrac- 
tion line produces a traveling (dynamic) 
wave on the surface, which subjects a 



structure first to tension, then compres- 
sion. However, in older, low-extraction 
mines, subsidence sags develop over a 
limited area governed by the mining and 
geological conditions of the site and the 
instability of the roof -pillar-floor sys- 
tem. Consequently, most sags in Illinois 
are caused by pillar crushing and/or set- 
tlement into the mine floor (14) . Thus a 
surface structure undergoes deformations 
defined by its position on the sag. In 
some cases, structures are subjected to 
several cycles of deformation caused by 
overlapping sags that develop in an area. 
In general, when subsidence occurs in a 
residential ajrea, most of the structures 
are located in the tension zone because 
its area is much larger than that of the 
compression zone (12). 




Southwest 



Profile curvature, lateral strain, 

deflection ratio, (A/L) and 

angular distortion (S/L) 

FIGURE 20. - Relationships between subsidence 
profile characteristics and ground deformations. 




FIGURE 21. - Comparison of subsidence profiles 
of radio station building and house C. No horizontal 
scale is indicated because no common origin exists 
f orboth structures. However, the length of each struc- 
ture is given so that a comparison can be made re- 
garding vertical displacement over the length of each 
structure. 



20 



The nature and intensity of structural 
deformations usually change along the 
length of the structure because of varia- 
tions in the ground surface displace- 
ments. The induced deformations and rig- 
id body movements can be estimated by 
parameters that described the subsidence 
profile along the length of the struc- 
ture. The profile parameters include the 
slopes at the lower (S^) and upper (S^) 
ends of the structure, the difference be- 
tween the lower and upper slopes (Sq), 
the angular distortion, the deflection 
ratio, and the curvature (fig. 20). 

Lateral ground displacement has the 
same pattern and is proportional to the 
profile slope. The magnitude of lateral 
strain along a section of profile can be 
related to the section curvature, which 
is estimated by dividing the difference 
in slope (Sq) at the ends of the section 
by the length (L) of the structure. The 
section curvature is also proportional to 
the deflection ratio which is used to es- 
timate the bending deformation (fig. 20). 

Angular distortion is used to estimate 
the induced vertical shear strains. It 
is calculated as the vertical distance 
between the profile tangent at the lower 
and upper ends of the structure along the 
subsidence profile (6) divided by the 
length (L) of the structure (fig. 20) . 
Rigid body rotations are not included in 
the angular distortion parameter. The 
induced tilt is a function of the profile 
slope. Induced rigid body horizontal and 
vertical displacements across the struc- 
ture are related to the differences 
in lateral displacement and differential 
settlement. 



The radio station building and house C 
were located in the tension zone of the 
same sag. A comparison of the subsidence 
profiles along both structures taken par- 
allel to the direction of horizontal 
ground movement is shown in figure 21. 
The subsidence profile along house C is 
much more severe than the profile along 
the radio station building. For example, 
the angular distortion along the house 
is 62.0 X 10~5 compared with 6.6 x 10"^ 
along the radio station building. Other 
profile parameters (table 2) also show 
that house C was subjected to more severe 
ground movements. 

Boscardin (32) has established damage 
criteria for masonry bearing wall struc- 
tures in terms of angular distortion 
and horizontal strain. Using his cri- 
teria and assuming only angular distor- 
tion, both structures fall into a "severe 
to very severe damage" category because 
both structures exhibit angular distor- 
tions of 6.6 X 10"^ or greater. Damage 
to both structures is also severe under 
visible damage and cost of repair cri- 
teria developed by Burland, Broms , and 
de Mello (17). Their classification sys- 
tem is given in table 3. 

The radio towers were subjected to a 
number of different subsidence events and 
sag interactions. The base of tower 2 
was tilted during both subsidences of sag 
2, and distortion occurred in all three 
towers as a result of tightening of the 
guy wires. Tightening occurred primarily 
when there was relatively little or no 
settlement of the tower bases. No estab- 
lished damage criteria for the response 
of these structures to ground movements 
were found in the literature. 



TABLE 2. - Summary of building damage and associated ground movements 



Radio station 
building^ 



House C2 



Slope, lower end of structure (SL)...pct 
Slope, upper end of structure (Su)...pct 

Slope difference (S^) = S^ - Sj pet 

Angular distortion 

Curvature ft"^ 



6.6 
2.3 



2.56 
1.18 
1.38 
10-3 
10-4 



62.0 
3.0 



8.50 
0.30 
8.20 
10-3 
10-4 



'Foundation consisted of wall footings; superstructure was made of 
concrete block, 1 story high. 

■^Foundation was brick basement walls and footings; superstructure 
was wood frame with exterior siding 2 stories high. 



21 



TABLE 3. - Classification of visible damage to walls, with particular reference to 
ease of repair 



Degree of 
damage 



Approx. crack 
width, 2 mm 



Description of typical damage^ (with ease of 
repair underlined) 



Negligible, . . 
Very slight. . 



Slight. 



Moderate. 



Severe. 



Very severe. . 




Hairline cracks. 

Fine cracks that can be treated easily during normal 
decoration . Perhaps isolated slight fracture in 
building. Cracks in external brickwork visible upon 
close inspection. 

Cracks easily filled. 



Redecoration probably required. 



Several slight fractures showing inside of building. 
Cracks are visible externally, and some repointing may 
be required externally to ensure weathertightness. 
Doors and windows may stick slightly. 

Cracks require some opening up and can be patched by a 
mason. Recurrent cracks can be masked by suitable 
linings. Repointing of external brickwork and possi- 
bly a small amount of brickwork to be replaced . Doors 
and windows sticking. Service pipes may fracture. 
Weathertightness often impaired. 

Extensive repair work involving breaking out and re- 
placing sections of walls, especially over doors and 
windows . Windows and door frames distorted, floor 

Walls learning or bulging notice- 
Service pipes 



sloping noticeably, 
ably; some loss of bearing in beams, 
disrupted. 
Requires major repair involving partial or complete 
reconstruction of building . Beams lose bearing; walls 
lean badly and require shoring. Windows broken from 
distortion. Danger of instability. 



^ In assessing the degree of damage, account must be taken of its location in the 
building or structure. 

2 Crack width is only one aspect of damage and should not be used on its own as a 
direct measure of damage. 

Source: Burland, Broms , and de Mello (17). 

SUMMARY 



To augment the characterization of mine 
subsidence over room-and-pillar mines in 
Illinois , the Bureau of Mines and the 
University of Illinois initiated an in- 
vestigation and evaluation of mine sub- 
sidence at Hegeler, IL. Detailed de- 
scriptions of the surface subsidence and 
the effects of the subsidence on struc- 
tures at the site have been presented. 

The site, in east-central Illinois, is 
covered with 29 to 47 ft of glacial 
till above 90 to 105 ft of bedrock. The 
mined Herrin (No. 6) coal is found 130 to 
135 ft below the surface and ranges from 
6,1 to 6,4 ft thick. The roof rock is 



composed of the Energy Shale that varies 
in thickness from 29 to 35 ft. The Her- 
rin (No. 6) coal was mined using a modi- 
fied room-and-pillar method with extrac- 
tion averaging 70 pet. The coal beneath 
the study site was mined from about 1960 
to 1967. 

Mine collapse caused three subsidence 
sags to form at the site. Sag 1 occurred 
in July 1967, sag 2 in May-June 1968, and 
sag 3 in November-December 1976. The 
mine failures causing the sags to form 
probably were initiated by pillar crush- 
ing or perimeter bearing failure of the 
pillars into the floor. 



22 



Subsidence sags 1 and 2 each formed as 
one major event, whereas sag 3 formed in 
two events, which occurred in 1976 and 
1978. The main subsidence movements for 
each sag took place within 2 months. The 
average diameter of the subsidence sags 
range from 280 to 430 ft with maximum 
settlements of 3.0 to 3.5 ft. When the 
sags are compared with other sags report- 
ed over room-and-pillar mines in Illi- 
nois, they show more severe subsidence 
profile characteristics even though the 
other mines have comparable subsidence 
factors and similar depths. 

Sag 1 severely damaged three houses and 
a radio station, broke numerous utility 
lines, and tensioned a guy wire to a 
transmitting tower. The radio station 
was subsequently repaired and remodeled; 
however, two of the houses were abandoned 
and removed in 1975, and the third house 
was removed in 1978. The maximum slope 
across the radio station building was 
0.022 and the curvature was 2.3 x lO""^ 
ft~1. The most severe profile character- 
istics were measured across house C where 
the slope was 0.07 and the curvature was 
3.0 X 10"'* ft"'. Angular distortions of 
6.6 X 10"^ and 62.0 x 10"^ were calcu- 
lated along the radio station building 
and house C, respectively. In two damage 
classifications, both structures were 
severely to very severely damaged. 

Sags 2 and 3 affected the three radio 
transmitting towers. The bases of towers 



1 and 2 settled 2.6 and 2.5 ft, respec- 
tively. The third tower base was not af- 
fected. The subsidence movements caused 
tensioning and loosening of the guy 
wires. Furthermore, the movements and 
drainage problems made the radial ground 
wire transmission systems ineffective. 
New ground wire transmission systems for 
towers 1 and 2 were installed, guy wires 
were replaced, and the areas around the 
base of the towers were drained and re- 
graded to prevent further water damage. 
The radio towers have been structurally 
damaged, primarily by bending and distor- 
tion from guy wire forces that were 
transmitted to the towers by ground move- 
ments that occurred outside the tower 
base. 

The observations and data obtained at 
the Hegeler site are instructive for 
characterizing the types of ground move- 
ment and structural damage that may occur 
over unstable room-and-pillar mines. 
Although precise presubsidence elevations 
were not known, sufficient information 
was available to confidently determine 
those conditions. Our understanding of 
subsidence and its effects on the ground 
surface and structures is limited because 
of the lack of available data. Observa- 
tion, collection, and interpretation of 
data will help us understand what to ex- 
pect when subsidence occurs and how best 
to respond to minimize its effects. 



REFERENCES 



1. Glover, T. 0. Surface Subsidence 
Due to Underground Coal Mining in Illi- 
nois. Pres. at SME/AIME Fall Meeting, 
St. Louis, MO, Oct. 19-21, 1977, SME/AIME 
preprint 77-F-324, 8 pp. 

2. Hunt, S. R. Surface Subsidence Due 
to Cal Mining in Illinois. Ph. D. The- 
sis, Univ. IL, Urbana, IL, 1980, 129 pp. 

3. Illinois State Geological Survey. 
Review of Underground Mining Practices in 
Illinois as Related to Aspects of Mine 
Subsidence With Recommendations of Legis- 
lation. IL Inst. Nat. Resour. , Doc. 80/ 
10, 1980, 145 pp. 

4. Nawrot, J. R. , R. J. Haynes , P. L. 
Pursell, J. R. D'Antuono, R. L. Sulli- 
van, and W. D. Klimstra. Illinois Lands 



Affected by Underground Mining for Coal. 
II Inst, for Environ. Quality, 1977, 195 
pp. 

5. Smith, W. H. , and J. B. Stall. 
Coal and Water Resources for Coal Conver- 
sion in Illinois. IL State Geol. Surv. 
Co-Op Res. Rept. , Nov. 4, 1975, 79 pp. 

6. Brauner, G. Subsidence Due to Un- 
derground Mining, Ground Movements and 
Mining Damage. BuMines IC 8572, 1973, 53 
pp. 

7. Grosboll, A. D. , and B. Valuikenas. 
Research Report and Recommendation for 
the Illinois House Executive Subcommittee 
on Mine Subsidence. IL Legislative Coun- 
cil, 1976, 37 pp. 



23 



8. Yarbrough, R. E. Effects of Mine 
Subsidence on Structures — Mine Subsidence 
Insurance Program in Illinois. Paper in 
Proc. Workshop on Surface Subsidence Due 
to Underground Mining (Morgantown, WV, 
Nov. 30-Dec. 2, 1981). WV University, 
Morgantown, WV, 1982, pp. 253-258. 

9. Bauer, R, A. Subsidence of Bed- 
rock Above Abandoned Coal Mines in Illi- 
nois Produces Few Fractures. Pres. at 
Soc, Min. Eng. AIME Fall Meeting, Den- 
ver, CO, Oct. 24-26, 1984, Soc. Min. Eng. 
AIME preprint 84-400, 8 pp. 

10. Bauer, R. A., and S. R. Hunt. 
Profile, Strain and Time Characteristics 
of Subsidence From Coal Mining in Illi- 
nois. Paper in Proc. Workshop on Surface 
Due to Underground Mining (Morgantown, 
WV, Nov. 30-Dec. 2, 1981). WV Univer- 
sity, Morgantown, WV, 1982, pp. 207-219. 

11. Bauer, R. A., and P. B. DuMon- 
telle. Disturbance of Overburden Bedrock 
by Coal Mine Subsidence in Illinois. 
Geol. Soc. Am. Ann. Meeting, Abs. with 
Programs, v. 15, No. 6, 1983, p. 523. 

12. Mahar, J. W. , and G. G. Marino. 
Building Response and Mitigation Measures 
for Building Damages in Illinois. Paper 
in Proc. Workshop on Surface Subsidence 
Due to Underground Mining (Morgantown, 
WV, Nov. 30-Dec. 2, 1981). WV Univer- 
sity, Morgantown, WV, 1982, pp. 235-252. 

13. Marino, G. G. , and J. W. Mahar. 
Response of Homes to Sag Subsidence Over 
Illinois Abandoned Coal Mines. Pres. at 
Soc. Min. Eng. AIME Annual Meeting, Los 
Angeles, CA, Feb. 26-Mar. 1, 1984. Soc. 
Min. Eng. AIME preprint 84-181, 1984, 
18 pp. 

14. DuMontelle, P. B., S. C. Bradford, 
R. A. Bauer, and M. M. Killey. Mine Sub- 
sidence in Illinois: Facts for the Home- 
owner Considering Insurance. IL State 
Geol. Surv. EGN 99, 1981, 24 pp. 

15. Mavrolas, P., and M. Schechtman. 
Coal Mine Subsidence: Proceedings From a 
Citizens' Conference. IL South Project, 
Inc., Herrin, IL, 1981, 45 pp. 

16. Burland, J. B., and C. P. Wroth. 
Settlement of Buildings and Associated 
Damage. Sec, in Settlement of Struc- 
tures. Wiley, 1974, pp. 611-654. 

17. Burland, J. B., B. B. Broms , and 
V. F. B. de Mello. Behavior of Founda- 
tions and Structures. Proc. 9th Int. 



Conf. on Soil Mechanics and Foundation 
Eng., Tokyo, sess. 2, 1977, pp. 495-546. 

18. Littlejohn, G. S. Monitoring 
Foundation Movements in Relation to Adja- 
cent Ground. Ground Eng., v. 6, No. 4, 
1973, pp. 17-22. 

19. Whittaker, B. N. , and A. G. Pasa- 
mehmetoglu. Ground Tilt in Relation to 
Subsidence in Longwall Mining. Int. J. 
Rock Mech. Min. Sci. and Geomech. Abs., 
V. 18, No. 14, 1981, pp. 321-329. 

20. Eveland, H. Pleistocene Geology 
of the Danville Region. IL State Geol. 
Surv. Rep. Inv. 159, 1951, 32 pp. 

21. Willman, H. B., E. Atherton, T. C. 
Buschbach, C. Collinson, J. C. Frye, 
M. E. Hopkins, J. A. Lineback, J. A. 
Simon. Handbook of Illinois Stratigra- 
phy. IL State Geol. Surv. Bull. 95, 
1975, 261 pp. 

22. Clegg, K. E. The LaSalle Anti- 
clinal Belt in Illinois. IL State Geol. 
Surv. Guidebook 8, 1970, pp. 106-110. 

23. Wanless, H. R. , J. B. Tubb, Jr., 
D. E. Gednetz, and J. L. Weiner. Map- 
ping Sedimentary Environments of Pennsyl- 
vanian Cycles. Geol. Soc. Am. Bull. , v. 
74, 1963, pp. 437-486. 

24. Kay, F. H. , and K. D. White. 
Coal Resources of District VIII (Dan- 
ville). IL Coal Min. Inv., Bull. 14, 
1919, 68 pp. 

25. Andros, S. 0. Coal Mining Prac- 
tice in District VIII (Danville). IL 
Coal Min. Inv., Bull. 2, 1914, 49 pp. 

26. Commercial-News (Danville, IL) . 
Radio Station WITY 'Sinking'. July 22, 
1967, pp. 1, 10. 

27. . 'I Heard a Noise in the 

Basement.' July 22, 1967, p. 3. 

28. . Radio Station Still Stand- 
ing. July 23, 1967, p. 21. 

29. . Sink Appears To Be Over. 

July 27, 1967, p. 17. 

30. Peng, S. S. Coal Mine Ground Con- 
trol. Wiley, 1978, 450 pp. 

31. Illinois State Geological Sur- 
vey. Subsidence at Hegeler, Illinois. 
Int. Field Rep., 1967, 9 pp. 

32. Boscardin, M. D. Building Re- 
sponse to Excavation Induced Ground 
Movements. Ph. D. Thesis, Univ. IL at 
Urbana-Champaign, Urbana, IL, 1980, 279 
pp. 



24 



APPENDIX. —CHRONOLOGICAL LIST OF EVENTS RELATED TO SUBSIDENCE AT HEGELER, IL 



Date and time 



Damage 



SUBSIDENCE SAG 1 



7/21/67: 

12:00 noon. 

2:00 p.m. . 

2:30 p.m. . 
11:30 p.m.. 



7/21/67: 

Afternoon to 
12 midnight. 



7/22/67: 

7:30 a.m. to 
12 midnight. 



7/23/67, 
10/67.. 



5/69 or 6/69 



Radio station damaged as follows: 
Doors began to stick. 
Large cracks developed in structure. 
Off the air for about 45 min. 
Off the air; noticed additional damage. 

Other damage as follows: 

0.17- to 0.25-ft-wide crack developed in pavement. 
At least 3 gas service lines broken; telephone lines pulled away 
from houses. 



Radio station damaged as follows: 
Back on the air. 

New cracks formed and existing cracks opened, 
to tower 1 was significantly tensioned. 



Southwest guy wire 



Other damage as follows: 

3 houses underwent additional serious damage due to subsidence; 
cracks in basements, separation of superstructure and foundation, 
distortion of superstructures, and utility damage. News accounts 
reported maximum settlement at about 4.0 ft. 

80 to 90 pet of damage to radio station building had occurred. 

Remodeling of radio station building began (movements appeared to 
have stopped). 

Separation and cracking of new addition to structure and to re- 
modeled radio station building. 



SUBSIDENCE SAG 2 



5/68 or 6/68.. .. 



5/69 or 6/69 



Radio station damaged as follows: 

Tower 1 settled 1.5 to 2.0 ft in 3 to 4 weeks, and 2.75 ft in 
6 weeks. Guy wires retensioned 3 times. Surface drainage 
noticeably affected. 

Water ponded around base of tower 1. 



SUBSIDENCE SAG 3 



11/76 or 12/76.. 

2/78 or 3/78 

7/78 



6/25/79, 



Tower 2 of radio station settled about 3 ft. Guy wires were re- 
tightened. Near failure of tower 2 (foundation tilted 0.5 ft to 
the east). 

Water ponded around base of tower 2 of radio station. 

Ground anchor of southwest guy wires on tower 3 settled. Top of 
tower bent. 

Tower 2 settled an additional 0.08 ft between 10/78 and this date. 



U.S. GOVERNMENT PRINTING OFFICE: 1986—605-017/40,025 



INT.-BU.OF MINES,PGH.,P A. 28 245 



H 20 1 



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Bureau of Mines— Prod, and Distr. 
Cochrans Mill Road 
P.O. Box 18070 
Pittsburgh, Pa. 15236 



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